A Novel Method for Assessing Left Bundle Branch Capture Using the Bidirectional Conduction Time Difference Between Left Bundle Branch Area Pacing and Coronary Sinus Leads

BACKGROUND: Left bundle branch area pacing (LBBAP) is an established conduction system pacing strategy; however, confirming left bundle branch (LBB) capture remains challenging. OBJECTIVE: We propose a novel method for LBB capture confirmation based on the bidirectional conduction time difference between the LBBAP and coronary sinus (CS) leads. METHODS: This observational study included 60 patients undergoing de novo left bundle branch-optimized cardiac resynchronization therapy. LBB capture was defined by (1) paced QRS transition, (2) LBB potential with current of injury, or (3) ΔV6 R-wave peak time ≥10 ms. LBBAP-to-CS and CS-to-LBBAP conduction times were measured. ΔLBB-CS ([CS-to-LBBAP] - [LBBAP-to-CS]) was compared between nonselective LBB pacing (NS-LBBP) and left ventricular septal pacing (LVSP). RESULTS: Among 60 patients (74.7±10.4 years; 42 men), 25 had left bundle branch block and 17 had non-specific intraventricular conduction delay. LBB capture was confirmed in 45 patients (75.0%). LBBAP-to-CS was 114.3±28.0 ms during NS-LBBP (n=43) and 134.2±19.0 ms during LVSP (n=29), whereas CS-to-LBBAP was 143.4±28.5 ms (n=60). ΔLBB-CS was greater during NS-LBBP than LVSP (27.5±9.9 vs. 7.9±7.4 ms, P<0.01). Receiver operating characteristic curve analysis identified a 21.5 ms cutoff for LBB capture (74.4% sensitivity; 100% specificity; area under curve [AUC] 0.95). In patients with baseline LBBB (n=25), a 20.5 ms cutoff for LBB capture yielded 92.9% sensitivity, 100% specificity, and an AUC of 0.99. CONCLUSION: ΔLBB-CS ≥ 21.5ms may serve as a novel adjunctive marker of LBB capture during LOT-CRT, with greater diagnostic accuracy at a 20.5 ms cutoff in patients with baseline LBBB.